1. Field of the Invention
The present invention relates generally to a method of providing Location Services (LCS) in an IP (Internet Protocol) Multimedia Subsystem (IMS)-based network environment, and in particular, to a method of providing LCS over an IMS network in a broadband wireless network.
2. Description of the Related Art
One of the reasons that an IMS network attracts great interest is that an IMS-based IP core network system provides a vision of the full convergence of wired and wireless services including future-generation mobile communications, Wireless Local Area Network (WLAN), and cable, as well as wired broadband Internet.
LCS is an application system and a service provisioning technology that accurately locates a person or an object over a mobile communication network and utilizes the accurate location. A 3rd Generation Partnership Project (3GPP) Technical Specification (TS) 22.071 notes “Location Services may be considered as a network provided enabling technology consisting of standardized service capabilities which enable the provisioning of location based applications”.
The implementation of LCS requires advanced positioning, positioning accuracy development, position processing in wireless Internet, spatial data processing, LCS platform-related technology, LCS application software development, an open geographic information system, LCS-related standardization, and LCS application service development. These technologies enable service providers to provide a variety of associated services such as information about surroundings, location tracking, safety, traffic information, delivery and navigation, and location advertisement.
FIG. 1 is a diagram illustrating a signal flow of an operation for providing LCS over a typical 3GPP network. Communications are conducted by Open Mobile Alliance (OMA) Mobile Location Protocol (MLP) between an LCS client and a Gateway Mobile Location Center (GMLC) (steps 131 and 153) and between GMLCs (steps 144 and 148). Communications between the GMLC and a Subscription Locator Function (SLF) and between the GMLC and a Home Location Register (HLR)/Home Subscriber System (HSS) (steps 134 to 139) are made via an IMS interface, Dh (interface between Requesting Location IMS-Interworking Function (LIMS-IWF) and SLF) or Sh (interface between LIMS-IWF and HSS/HLR), or by Media Access Protocol (MAP). The GMLC is interfaced with a 3G network element such as a Serving General Packet Radio Service (GPRS) Support Node (SGSN) by MAP (steps 145 and 147).
Referring to FIG. 1, when an LCS client 100 wants to locate a target User Equipment (UE) 120, he transmits an LCS Service Request message to a home LIMS-IWF 106 via a requesting GMLC 102 and a requesting LIMS-IWF 104 in steps 131, 132 and 133.
The requesting GMLC 102 manages an external interface to provide LCS. For example, it is responsible for authentication of an external LCS client, mobility management, determination of the position accuracy of final position estimation for retry and reject, and coordinates transformation for identification of the LCS client. The LIMS-IWF, located within the GMLC, is an interworking function for supporting LCS based on IMS. To obtain the location information of a UE using an IMS Public User Identity (i.e. Session Initiation Protocol-Uniform Resource Identifier (SIP-URI)) in an existing packet-switched network, the LIMS-IWF acquires the Mobile Subscriber ISDN (MSISDN) of the UE.
The LCS Service Request message is defined with MLP. It carries the ID of the target UE be located (SIP-URI in the IMS network), an LCS type (Immediate or Conditional), LCS requirements, the ID of the UE requesting the location information, and authentication information.
The home LIMS-IWF 106 gets the address of an HLR/HSS 110 to which the UE 120 has been registered by querying an SLF 108 via a Dh interface (Dh-SLF) in steps 134 and 135. When two or more HSSs/HLRs reside within the network and they are identified by different addresses, the SLF 108 provides the address of the HSS/HLR 110 to which the UE 120 has been registered.
The home LIMS-IWF 106 then retrieves the MSISDN of the target UE 120 having an SIP-URI from the HSS/HLR 110 via an Sh interface (Sh-PULL) in steps 136 and 137.
The HSS/HLR 110 manages LCS subscription information and location information for terminated routing, to thereby track access. It also provides user profile information directly or via a server and performs authentication.
In steps 138 and 139, the home LIMS-IWF 106 retrieves the network ID of a home GMLC 112 using a MAP message with the MSISDN of the UE 120. The home LIMS-IWF 106 forwards the LCS Service Request message to the home GMLC 112 according to the network ID in step 140.
In step 141, the home GMLC 112 performs a privacy check to determine whether the LCS client 100 is allowed to locate the UE 120. If the privacy check passes, i.e. permission is granted to locate the UE 120, the home GMLC 112 queries the HSS/HLR 110 using a Send Routing Info for LCS message being a MAP message with the MSISDN of the UE 120 to get the address of a visited GMLC 114 in step 142. The HSS/HLR 110 transmits the network ID of the visited GMLC 114 to the home GMLC 112 by a Send Routing Info for LCS Ack message being a MAP message in step 143.
The home GMLC 112 forwards the LCS Service Request message to the visited GMLC 114 according to its network ID in step 144. In step 145, the visited GMLC 114 translates the LCS Service Request message to a Location Request message in the form of a Radio Resource LCS Protocol (RRLP) message and transmits the Location Request message to an SGSN 116. The SGSN 116 contains functionality responsible for management of LCS routing information and authentication of LCS subscribers. The SGSN 116 forwards the Location Request message to the UE 120 via a Base Station System (BSS) 118 and measures the location of the UE 120 in step 146.
After the location measurement, the SGSN 116 notifies the LCS client 100 of the location of the UE 120 by an LCS Service Response message in steps 147 to 153. During the transmission of the location information of the UE 120, the home GMLC 112 performs a privacy check to determine whether the LCS client 100 is allowed to locate the UE 120 in step 149. Only when the privacy check passes, the subsequent steps are carried out.
FIG. 2 is a diagram illustrating a signal flow of an operation for providing a conditional LCS over the typical 3GPP network. The conditional LCS is a location service contingent on some current or future event specified by an LCS client. Only when the event occurs, the location information of a target LE is provided to the LCS client.
Referring to FIG. 2, when an LCS client 200 wants to locate a target LE 214, he transmits an LCS Service Request message to a requesting GMLC 202 in step 221. The LCS Service Request message is defined with MLP. It carries the ID of the target UE (SIP-URI), an LCS type (Immediate or Conditional), LCS requirements, the ID of the UE requesting the location information, and authentication information. The SIP-URI is an IMS public user ID.
In step 222, the requesting GMLC 202 forwards the LCS Service Request message to a visited GMLC 208 via a home GMLC 204 and an HLR/HSS 206 in the same manner as in steps 134 to 144 of FIG. 1.
The visited GMLC 208 requests the location information of the UE 214 to a Mobile Switching Center (MSC)/SGSN 210 by a Provide Subscriber Location message being a MAP message in step 223. The MSC/SGSN 210 contains functionality responsible for management of LCS routing information, and control of authentication of LCS subscribers and LCS provisioning.
The MSC/SGSN 210 locates the LE 214 via a Random Access Network 212 and performs operations needed to communicate with the UE 214, including authentication, in step 224. If a connection is established to the LE 214, the MSC/SGSN 210 transmits an LCS Area Event Invoke message to the UE 214 to indicate that an LCS area event has been set in step 225. In steps 226 to 230, the UE 214 transmits an LCS Service Response message to the LCS client 200, notifying of an acknowledgement for the invoked LCS area event. For example, the LCS area event to be reported is the LE 214 being in an area set by the LCS client 200 (e.g. Cupertino in Santa Clara County).
If the area event occurs, for example, the UE 214 enters Cupertino in Santa Clara County in step 231, the UE 214 transmits its location information to the LCS client 200 by an LCS Service Response message in steps 232 to 238. If the UE 214 moves and thus a network element managing the location information of the UE 214 is changed, the home GMLC 204 retransmits the LCS Service Request message to the changed network element to which the UE 214 is now registered in step 235. During the transmission of the location information of the UE 214, the home GMLC 204 performs a privacy check to determine whether the LCS client 200 is allowed to locate the UE 214 in step 236. Only when the privacy check passes, the subsequent steps are carried out.
As described above, the MLC and the 3G network communicate with each other via the MAP interface to provide LCS. However, implementation of the MAP interface for LCS is inefficient to a network that provides an IP multimedia service independently of a bearer network.
Moreover, when the UE roams and the network element managing its location information is changed in the conditional LCS, the GMLC inconveniently has to retransmit the LCS Service Request message to the new network element.